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2003 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Data Privacy and Security

verfasst von: David Salomon

Verlag: Springer New York

Enthalten in: Professional Book Archive

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Über dieses Buch

Covering classical cryptography, modern cryptography, and steganography, this volume details how data can be kept secure and private. Each topic is presented and explained by describing various methods, techniques, and algorithms. Moreover, there are numerous helpful examples to reinforce the reader's understanding and expertise with these techniques and methodologies.

Features & Benefits:

* Incorporates both data encryption and data hiding

* Supplies a wealth of exercises and solutions to help readers readily understand the material

* Presents information in an accessible, nonmathematical style

* Concentrates on specific methodologies that readers can choose from and pursue, for their data-security needs and goals

* Describes new topics, such as the advanced encryption standard (Rijndael), quantum cryptography, and elliptic-curve cryptography.

The book, with its accessible style, is an essential companion for all security practitioners and professionals who need to understand and effectively use both information hiding and encryption to protect digital data and communications. It is also suitable for self-study in the areas of programming, software engineering, and security.

Inhaltsverzeichnis

Frontmatter

Introduction

Introduction
Abstract
On 17 January 1917, the British government had intercepted an encrypted German telegram and sent it, following routine procedures, to Room 40, Britain’s cipher bureau, for decipherment. Just by glancing at it, the British cryptanalysts realized that it was encrypted with a code used only for high-level diplomatic communications, and immediately proceeded to decipher it. In just a few hours, using knowledge gained from similar decipherments in the past, the codebreakers were able to decipher parts of the telegram. Even when only partially deciphered, it was clear from its contents that the telegram contained a secret German plot, devised to discourage the United States from joining the (first World) War. Once fully deciphered and brought to the attention of the American government and public, this telegram, more than anything else, influenced the United States’ decision to enter the war, thereby significantly affecting world history.
David Salomon

Data Encryption

Frontmatter
1. Monoalphabetic Substitution Ciphers
Abstract
A cipher where each symbol is replaced by another symbol, where the replacement does not vary, is called a monoalphabetic substitution cipher.
David Salomon
2. Transposition Ciphers
Abstract
In a substitution cipher, each letter in the plaintext is replaced by another letter. In a transposition cipher, the entire plaintext is replaced by a permutation of itself. If the plaintext is long, then each sentence is replaced by a permutation of itself. The number of permutations of n objects is n!, a number that grows much faster than n. However, the permutation being used has to be chosen such that the receiver will be able to decipher the message. [Barker 92] describes a single-column transposition cipher.
David Salomon
3. Polyalphabetic Substitution Ciphers
Abstract
Perhaps the simplest way to extend the basic monoalphabetic substitution codes is to define two cipher alphabets and use them alternately. In the example below, the first letter S of the plain message SURRENDER is replaced by D from cipher alphabet 1, but the second letter U is replaced by D from cipher alphabet 2. The same cipher letter D replaces two plaintext letters. Similarly, the two cipher letters Q and L stand for the plain letter A. This primitive polyalphabetic substitution cipher, developed by the Renaissance figure Leon Battista Alberti, is already much safer than any monoalphabetic cipher. (The same Alberti also constructed a simple cipher disk, similar to the one shown in Figure 5.1, that’s the predecessor of all the many rotor encryption machines that followed. See Section 5.1.)
David Salomon
4. Random Numbers
Abstract
The discussion on pages 67 and 88 makes it clear that the use of random keys can lead to encryption with absolute security. When a long, random key is used, the Vigenère method (and also other polyalphabetic ciphers) produces ciphertext with a uniform distribution of letters. The only way to decipher such ciphertext, even if the encryption method is known, is to try all possible keys. This, however, is impractical even with the help of a fast computer. Even if a very fast computer can generate the plaintexts for all the possible keys in a reasonable amount of time, a person would still have to go over each plaintext to see whether it makes sense. The computer may be programmed to check each plaintext as it is being generated and reject it if it looks random or if it consists mostly of phrases that are not in the dictionary. Such an automatic check, however, would still leave too many plaintexts for a human to examine.
David Salomon
5. The Enigma
Abstract
Encrypting a long message by hand is a slow, tedious, and error-prone process. Cryptographers have always felt the need for the mechanization of secrecy and have constructed machines and instruments of various types to produce fast, reliable encryption. This chapter concentrates on the most famous of those machines, namely the German Enigma, used during the Second World War. Following a short discussion of simple rotor encryption machines (Section 5.1), the bulk of this chapter describes the history of the Enigma and its principles of operation. The story of breaking the Enigma code, a classical case study of codebreaking, is told in Section 5.4.
David Salomon
6. Stream Ciphers
Abstract
The encryption methods discussed in previous chapters assume that the plaintext consists of letters and digits. With the development of the modern digital computer which uses binary numbers, secure codes had to be based on bits. If the plaintext is text, then it is represented internally either in ASCII, with eight bits per character (seven code bits and one parity bit) or in Unicode, with 16 bits per character.
David Salomon
7. Block Ciphers
Abstract
A block cipher encrypts a message by breaking it up into (normally equal-size) blocks. encrypting each block independently of the other blocks, and turning each block of plain-text (plainblock) into a block of ciphertext (cipherblock) that has the same size. The same algorithm is used to encrypt all the blocks, and this algorithm should preferably be reversible. A reversible algorithm simplifies any implementations (software or hardware) because the same processes used to encrypt a block can also be used to decrypt it. It is possible to generate cipherblocks that are shorter than the plainblocks by simply using a compression method to compress the ciphertext once it has been created. It is also possible to end up with cipherblocks longer than the plainblocks by adding parity bits or employing any error-detection or error-correction code. However, cryptography, compression, and reliable codes are three separate disciplines, so modern cryptography limits itself to securing data.
David Salomon
8. Public-Key Cryptography
Abstract
The problem of key distribution has been mentioned many times in this book. For many years it was strongly believed that this problem has no satisfactory solution, but in the 1970s, an ideal, simple solution was found and has since become the foundation upon which much of modern cryptography is based.
David Salomon
9. Quantum Cryptography
Abstract
Today, RSA cryptography is the last word in secure codes. Present-day computers are not fast enough to factor large numbers, and therefore cannot break RSA-encrypted messages. In the future, however, this situation may change. After hundreds of years of effort, no efficient factoring algorithm has been found, so the chance that such an algorithm exists seems slim. However, until it is proved that such an algorithm does not exist, the possibility that it exists and will some day be discovered, with disastrous results for RSA, cannot be ruled out. Another possibility is the development of a new type of computers (perhaps quantum computers, see http://www.qubit.org/), many orders of magnitude faster than today’s computers, that would be able to factor large numbers in reasonable time even with an inefficient factoring algorithm.
David Salomon

Data Hiding

Frontmatter
10. Data Hiding in Text
Abstract
Today, in the digital age, any type of data, such as text, images, and audio, can be digitized, stored indefinitely, and transmitted at high speeds. Notwithstanding these advantages, digital data also have a downside. They are easy to access illegally, tamper with, and copy for purposes of copyright violation.
David Salomon
11. Data Hiding in Images
Abstract
Virtually all sophisticated steganographic methods hide a message by embedding it as low-level noise in an image or audio file which then becomes the cover file. This approach has two disadvantages: the information hiding capacity of a cover file is small, so a large cover file is needed to hide a substantial amount of data; and once data are hidden in an image or audio file, any lossy compression destroys the embedded data. It seems that such an image should be compressed with lossless compression only, but this chapter shows how secret data can be hidden even in a lossily compressed image.
David Salomon
12. Data Hiding: Other Methods
Abstract
Starting with Section 12.2, this chapter discusses data hiding in an MPEG-2 video file. This is followed with audio steganography. Starting with Section 12.3, the basics of digital audio and the properties of the human auditory system are described, following with audio steganography in the time domain. Next, the chapter introduces (in Section 12.7) the concept of the steganographic file system. The last part of the chapter is a short discussion of the limits of steganography (Section 12.8) and the prospect of public-key steganography (Section 12.9).
David Salomon
Backmatter
Metadaten
Titel
Data Privacy and Security
verfasst von
David Salomon
Copyright-Jahr
2003
Verlag
Springer New York
Electronic ISBN
978-0-387-21707-9
Print ISBN
978-1-4419-1816-1
DOI
https://doi.org/10.1007/978-0-387-21707-9